It is known to etch metallic, e.g., copper, workpieces with a liquid, e.g., an ammonium acid, by passing the workpiece through a treatment tank in which the etchant liquid is sprayed over the workpiece. The liquid draining off the workpiece falls into a sump at the bottom of the etchig tank and is recirculated by a pump. Thereafter the workpiece passes into a rinsing tank where it is rinsed with a liquid such as fresh water which is sprayed and recirculated like the etchant liquid.
The principal disadvantage of such systems is that the etchant liquid is continuously weakened, while at the same time the rinse liquid becomes increasingly contaminated. For this reason it is necessary to periodically drain off part of the etchant liquid and replace it with full-strength etchant in order to maintain proper strength. In the same manner part of the rinse liquid is replaced with fresh water, with a filter normally being interposed in the circulation system for the rinse liquid. Thus it is necessary to dispose of the drawn-off portions of etchant liquid and rinse liquid. Since both of these liquids are contaminated with metal particles and acids it is necessary to neutralize and purify them before disposal, a costly operation that greatly increases the overall expense of etching.